Chiral smectic liquid crystal device

ABSTRACT

A liquid crystal device having a first substrate on which a first group of belt-shaped electrodes are formed, a second substrate on which a second group of belt-shaped electrodes are formed so as to cross the first group of belt-shaped electrodes, and a chiral smectic liquid crystal arranged between the first and second substrates, wherein a first orientation film formed on the first group of belt-shaped electrodes and second orientation films formed in spaces among the belt-shaped electrodes are different.

This application is a division of application Ser. No. 07/828,123, filedJan. 30, 1992 U.S. Pat. No. 5,303,076.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a device using a chiral smectic liquid crystalwhich exhibits ferroelectricity and also relates to a display apparatus.

2. Related Background Art

With respect to a display apparatus using a ferroelectric chiral smecticliquid crystal, there have been known display apparatuses in each ofwhich a ferroelectric chiral smectic liquid crystal (hereinafter,referred to as an FLC) is injected in a liquid crystal cell which isconstructed by arranging two glass substrates in which transparentelectrodes are formed on inner surfaces and an orienting process hasbeen performed so as to face each other while keeping a cell gap ofabout 1 to 3 μm as disclosed in, for instance, U.S. Pat. Nos. 4,639,089,4,681,404, 4,682,858, 4,712,873, 4,712,874, 4,712,875, 4,712,877,4,714,323, 4,728,176, 4,738,515, 4,740,060, 4,765,720, 4,778,259,4,796,979, 4,796,980, 4,859,036, 4,932,757, 4,932,758, 5,000,545, and5,007,716, and the like.

Among the above background arts, in particular, a device in which theFLC is oriented by forming a chevron structure shown in FIG. 1 hasexcellent light state under a cross nicols, so that an enough largecontrast is obtained. FIG. 1 shows a cross sectional view of anorienting state of the FLC arranged between substrates 11 and 12. An LFC13 forms a layer 15 comprising a plurality of liquid Crystal molecules14. A plurality of layers 15 are aligned in the same direction and astructure in which the layers 15 are bent occurs. At this time, it ispreferable that the major axis of the liquid crystal molecule 14 isinclined for the substrates 11 and 12 at a pretilt angle of, preferably,5° or more. As for the above aligning state, it is desirable that theorienting process is performed to the substrates 11 and 12 by rubbings16 and 17 in the same direction.

FIG. 2 is a plan view of the device in which the FLC 13 of the abovechevron structure is formed. Reference numeral 21 in FIG. 2 denotes asealing material to seal the substrates 11 and 12. Although not shown,in the above device, a plurality of a first group of belt-shapedelectrodes to apply a voltage are arranged on the substrate 11, and aplurality of second group of belt-shaped electrodes are arranged on thesubstrate 12 so as to cross the first group of belt-shaped electrodes,thereby forming matrix electrodes. A normal line 22 (On a plane surface)of the layer 14 of the FLC 13 is substantially parallel with the rubbingdirections 16 and 17. In the device shown in FIG. 2, the liquid crystalmolecules 14 are uniformly tilted to the left (on the plane surface) atan angle of +θ (spontaneous polarization is set to a polarity directingfrom the upper portion of the paper surface to the lower portion).

According to the experiments by the inventors et al., by applying avoltage (for instance, AC voltage of ±8 volts at 10 Hz) across the upperand lower electrodes of the above matrix electrodes under such a state,the liquid crystal molecules 14 start flowing toward the right side inthe layer 15. When such a voltage is continuously applied for a longtime (for instance, 20 to 50 hours), as shown in FIG. 3, a region 31 inwhich the number of liquid crystal molecules 14 has decreased or whichhas been depleted occurs in the left side portion. On the other hand, aregion 32 in which the number of liquid crystal molecules 14 hasincreased is formed in the right side portion. The inventors et al.consequently have found out a problem such that an interference colorappears over the whole plane surface of the device and the displayquality is lost.

In the case where the liquid crystal molecules 14 in FIG. 2(c) aretilted to the right (on the plane surface) at an angle of -θ(spontaneous polarization is set to a polarity directing from the lowerportion on the paper surface to the upper portion), it has been alsofound out that the liquid crystal molecules start flowing toward theleft side on the contrary to the above case.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a liquid crystal device or adisplay apparatus which can solve or suppress the above problems.

According to the invention, there is provided a liquid crystal devicehaving a first substrate on which a first group of belt-shapedelectrodes are formed, a second substrate on which a second group ofbelt-shaped electrodes are formed so as to cross the first group ofbelt-shaped electrodes, and a chiral smectic liquid crystal arrangedbetween the first and second substrates, wherein a first orientationfilm provided on the first group of belt-shaped electrodes and secondorientation films provided in spaces among the belt-shaped electrodesare different.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing a liquid crystal aligning stateused in the invention;

FIG. 2(a) is a plan view of FIG. 1;

FIG. 2(b) is an enlarged plan view of FIG. 2(a);

FIG. 2(c) is an enlarged plan view of FIG. 2(b);

FIG. 3 is a plan view showing a state in the case where a conventionaldevice is used;

FIG. 4(a) is a plan view showing a device of the invention;

FIG. 4(b) is a plan view of a substrate 12 used in the device of theinvention;

FIG. 5 is a block diagram of a display apparatus of the invention; and

FIGS. 6 and 7 are waveform diagrams showing driving waveforms used inthe invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the invention is shown in FIG. 4. The substrate 11 inFIG. 4 is constructed by: a glass substrate 40a; a first group ofbelt-shaped electrodes 41a; a film 42a of an inorganic insulatingmaterial such as tantalum oxide (Ta₂ O₅) or the like; and a homogeneousorientation film 43a such as a polyimide film which has been rubbingprocessed. The substrate 12 is constructed by: a glass substrate 40b; asecond group of belt-shaped electrodes 4lb (which cross the belt-shapedelectrodes 41a); a film 42b of an inorganic insulating material such astantalum oxide (Ta₂ O₅) or the like; an orientation film 43b such as apolyimide film (the same kind as the orientation film 43a) which hasbeen rubbing processed; and homeotropic orientation films 44 arranged inspaces among the belt-shaped electrodes 41b.

The first group of belt-shaped electrodes 41a and the second group ofbelt-shaped electrodes 41b are formed by transparent conductive filmshaving thicknesses in a range from 300 Å to 3000 Å. In addition to Ta₂O₅, TiO₂, SnO₂, or the like can be used as a film of the inorganicinsulating material and such a film is formed so as to have a thicknesswithin a range from 500 Å to 5000 Å.

The homeotropic orientation film 44 can be formed by a film of ahydrocarbon compound containing fluorine or silane compound containingfluorine such as fluorochloromethane, fluorochloroethane,fluoromethoxysilane, fluoroethoxysilane, or the like. It is preferableto set a film thickness to a value within a range from 10 Å to 1000 Å.

In the device shown in FIG. 4, the FLC 13 existing in the intersectingportion between the first group of belt-shaped electrodes 41a and thesecond group of belt-shaped electrodes 41b is in an aligning state ofthe chevron structure shown in FIG. 1. On the other hand, the FLC in thenon-intersecting portion is influenced by the homeotropic orientationfilms 44 and causes an aligning state different from the chevronstructure.

According to the invention, the orientation films of the same kind asthat of the homeotropic orientation films 44 are arranged in the spacesamong the second group of belt-shaped electrodes 41b so as to come intocontact with the FLC 13, so that the foregoing problems can be furthersolved or suppressed.

FIG. 5 is a block diagram illustrating a structural arrangement of anembodiment of the display apparatus according to the present invention.A display panel 51 (shown in FIG. 4) is composed of scanning electrodes52, data electrodes 53, and an FLC having the chevron structure shown inFIG. 1 and disposed therebetween. The orientation of the ferroelectricliquid crystal is controlled by an electric field at each intersectionof the scanning electrodes and data electrodes formed due to voltagesapplied across the electrodes.

The display apparatus includes a data electrode driver circuit 54, whichin turn comprises an image data shift register 541 for storing imagedata serially supplied from a data signal line 56, a line memory 542 forstoring image data supplied in parallel from the image data shiftregister 541, a data electrode driver 543 for supplying voltages to thedata electrodes 53 according to the image data stored in the line memory542, and a data side power supply changeover unit 544 for changing overamong voltages V_(D), 0, and -V_(D) supplied to the data electrodes 53based on a signal from a changeover control line 511.

The display apparatus further includes a scanning electrode drivercircuit 55, which in turn comprises a decoder 551 for designating ascanning electrode among all of the scanning electrodes based on asignal received from a scanning address data line 57, a scanningelectrode driver 552 for applying voltages to the scanning electrodes 52based on a signal from the decoder 551, and a scanning side power supplychangeover unit 553 for changing over among voltages V_(S), 0, and-V_(S) supplied to the scanning electrodes 52 based on a signal from thechangeover control line 511.

The display apparatus further includes a CPU 58, which receives clockpulses from an oscillator 59, controls an image memory 510, and controlsthe signal transfer over the data signal line 56, scanning address dataline 57, and changeover control line 511.

FIG. 6 shows a set of drive voltage signal waveforms used in the presentinvention. In one scanning selection period, a scanning selection signalhaving alternating voltages ±V_(S) and a voltage 0 is applied to ascanning electrode, wherein the voltages ±V_(S) and the voltage 0 arevalues defined with reference to the voltage level of a scanningnon-selection signal. The data electrodes are supplied with a black orwhite data signal depending on given data. In the embodiment, the pixelson a scanning electrode supplied with a scanning selection signal aresimultaneously erased into a black state in a period T₁ during onescanning selection period, and then in a subsequent period T₂, a pixelsupplied with a data signal (B) is set to a black state and a pixelsupplied with a data signal (W) is set to a white state.

In the apparatus of the present invention, temperature compensation maybe effected by modulating (changing) the length of one scanningselection period (1H) and the magnitude of a drive voltage peak valueV_(OP) (capable of writing in black or white) which is V_(OP1) orV_(OP2) giving a maximum value during the period T₂.

FIG. 7 is a waveform diagram showing an example of a sequence ofapplying a scanning selection signal shown in FIG. 6 to the scanningelectrodes. According to the scanning sequence shown in FIG. 7, ascanning selection signal is sequentially applied to the scanningelectrodes S₁, S₂, . . . , S_(F8+8)(s-1) every 8th electrode (7electrodes apart) in one vertical scanning (field scanning) and onepicture is formed through 8 times of field scanning to complete oneframe scanning. In this instance, in each field scanning, the scanningselection signal is also applied to the scanning electrodes S_(A) andS_(B) in the non-display region. In FIG. 7, the symbols F₁, F₂, . . . ,F₈ each represents an ordinal number of field scanning in one framescanning and the symbol s represents an ordinal number of scanning inone field scanning.

A series of experiments were conducted wherein the above-mentioneddisplay operation was repeated by using a ferroelectric liquid crystalpanel with the dimensions and drive conditions as shown below and thedriving signal waveforms shown in FIGS. 6 and 7 while applying thescanning selection signal to the scanning electrodes 52 electrodes apart(in every 8th electrode).

What is claimed is:
 1. A method for producing a chiral smectic liquidcrystal device comprising first and second substrates provided withfirst and second groups of belt-shaped electrodes arranged to cross eachother, said method comprising the steps of:providing the first group ofbelt-shaped electrodes on one surface of the first substrate; providinga film formed by a hydrocarbon compound containing fluorine or silanecompound containing fluorine in a space among the first group ofbelt-shaped electrodes on one surface of the first substrate; providinga rubbed polyimide film on the first group of belt-shaped electrodes;providing the second group of belt-shaped electrodes on one surface ofthe second substrate; providing a film formed by a hydrocarbon compoundcontaining fluorine or a silane compound containing fluorine in a spaceamong the second group of belt-shaped electrodes on one surface of thesecond substrate; and providing a rubbed polyimide film on the secondgroup of belt-shaped electrodes.
 2. A method according to claim 1,further comprising a step of forming an inorganic insulating filmbetween said first group of belt-shaped electrodes and said rubbedpolyimide film.
 3. A method according to claim 1, wherein the chiralsmectic liquid crystal provided at an intersection between said firstand second groups of belt-shaped electrodes has an orientation state ofa chevron structure.
 4. A method according to claim 1, wherein thechiral smectic liquid crystal not provided at an intersection betweensaid first and second groups of belt-shaped electrodes has anorientation state of non-chevron structure.
 5. A method according toclaim 1, wherein said film formed by polyamide compound containingfluorine or silane has a thickness of 10-1000 Å.